I would not expect you to be anywhere close to $3000 if you spend $2500 on the short block unless you sell the 340. And if you are really going to hammer on this block, then I am skeptical on any mass production bought short block.
If you need to stick with that budget, then you can do a lot if you can do most of the work. Some rough numbers which are just pulled out of my head..
1) Tear down and inspect the block, have it cleaned, measured, and see if it will hone OK with no new boring. If boring is needed, go .020" over. $200-500
2) Buy new Speed Pro L2316F pistons; the L2316F pistons will not require a rebalance of the crank. I can only see them in .020" oversize not standard at this point. This will get your CR up to a real mid 9 range, and that will be good. $450 with rings
3) Keep crank as is and check. Hope all is OK. Have rods checked and put in new rods bolts. $200-$250
4) New main and rod bearings, cam bearings, decent timing chain, oil pump shaft, and oil pump. $300
5) New stock lower gasket set with 1121G thin head gaskets. $100
6) New damper for reliability $250
If you can assemble yourself, then you are in the $1700-1800 range with forged pistons and a high quality damper for revving, and that is less than for the short block with ??? pistons, and no or standard damper.
Now you have the cam and springs and lifters; plan at least $300.
Assume the valve train does not need a lot of work and you run heavy duty stock rockers. $180
Now you are at about $750 left for the heads. If the miles are really low, I'd hope that no guides are needed. If so then you are home free with a few hundred bucks of head work. You can port yourself as you seem to have indicated.
400 HP? I doubt it; the heads don't have it without some work; if you you could kick in another $750-$1000 budget, then you are at a new bolt-on set of really good heads. But focus on torque, not HP, for what you are doing. That will all be in the cam selection and tune. I'd stick with the DP carb for sure and reconsider the torque converter and move up a step from the stock one.
